X-ray angiography is performed to obtain an image of a vascular structure of a patient. An angiography enables a healthcare practitioner to obtain an image of particular blood vessels that supply blood to major organs such as the heart and brain, for example. Once obtained, the healthcare professional is able to review the flow of blood through the target vascular structures for diagnostic purposes. For example, angiographic images enable a healthcare professional to diagnose pathology of vessels such as blockage caused by plaque build up.
Angiographic x-ray imaging operates similarly to conventional x-ray in that x-rays are generated by an x-ray tube and as they pass through the body part being imaged, they are attenuated (weakened) at different levels. These differences in x-ray attenuation are then measured by a detector and the resulting image is recorded. The images are recorded successively thereby providing a series of moveable images able to viewed by the practitioner over time enabling the practitioner to evaluate the flow of blood through the target vasculature. The series of images, sometimes referred to as an angiography scene, are either viewed in real time on a display or stored for later review and evaluation. Angiography differs from conventional x-ray procedures in that during an angiography, a stream of contrast agent (dyes) is injected into the vessels to create detailed images of the vessels in real time.
Digital subtraction angiography (DSA) is a computer-aided image processing method used to enhance vasculature images in which each pixel of data acquired in an x-ray angiography procedure is digitized. DSA relies on the comparison between images taken immediately preceding an injection of a contrast bolus (mask image) and those obtained as the contrast bolus is passing through the target vessels (contrast image). The mask image is digitally subtracted from each of the contrast images resulting in the contrast-filled vessels being rendered on a display free of the background detail contained in the mask image. Additional known image processing functions for further enhancing the final images are performed to produce a series of successive images which are then replayed sequentially enabling a healthcare practitioner to visualize fluid flow through the target vessels.
When studying the contrast flow of fluid through vessels in an angiography scene, it is useful to build a static representation of the flow using a color spectrum to represent the time at which contrast reached a certain state within the vessels (e.g., first entered, reached a peak, no longer seen). However, a drawback associated with this type of visualization is that only a small time window of the entire acquisition may be of interest. A system according to invention principles addresses these deficiencies and related problems.